A smoke detector is a device that detects smoke and issues an alarm to alert nearby people that there is a potential fire. Because smoke rises, most smoke detectors are mounted on the ceiling or on a wall near the ceiling. Virtually all modern smoke detectors come equipped with a test button that activates a test function. The purpose of the test function is to provide a means to test the power supply and/or the associated detection circuitry prior to actual smoke having been detected. Such testing is may be used to verify that the smoke detector is working properly. Such detection circuitry usually includes a manually operable push button switch for the purpose of initiating the detector test function.
Some smoke detectors include an integrated photosensor. A control beam of incident electromagnetic energy can be provided from a remotely located portable source such as a flashlight. Directing the beam of radiant energy from the flashlight against the smoke detector's photosensor causes the smoke detector to initiate a test sequence.